Manufacture of water-laid felts



Patented Jan. 8, 1935 PATENT OFFICE 1,987,213 MANUFACTURE or WATER-LAID FELTS George A. Richter, Berlin, N. 11., assignor to Brown Company, Berlin, N.'H;, a corporation of Maine No- Drawing.

Application December 10, 1932,

Serial No. 646,740

12 Claims.

This invention relates to the manufacture of absorptive papers or water-laid felts designed more particularly for impregnation purposes.

In the manufacture of impregnated sheet prod 6 ucts, it is sometimes the practice to use as the base-sheet one which has been felted on machinery of the paper-making type. While various kinds of fibrous material maybe employed as the felt-making furnish, it has heretoforebeen the practice in some industries, .notably the roofing and floor-covering industries, to use as the raw material, waste rags ofvarious descriptions. These rags are conditioned for the felt-making operation in a so-called hollander or beater engine, wherein they are beaten in the presence of water for the purpose of disintegrating the pieces of cloth until there is produced a pulp or half-, stuff made up of fibers whose size is such as to permit their felting on a paper-making machine intoa sheet of uniform texture. In some in-- stances, the raw rags, as they are purchased on the open market, are subjected to a purifying or cleansing treatment in dilute alkaline solutions at elevated temperatures and are then washed free of the solution, before they are subjected to beater action. In any case, however, the beating.

absorptivity, softness, and flexibility of the felt,

even though it enhances such physical qualities as strength and tear resistance.

In accordance with the present invention, therefore, the reduction of rags in water to form a pulp or halfstuff suitable for the felt-making operation on a paper-making machine is accomplished while preserving the pulp in a substantially unhydrated or free state. This result is had by converting the raw rag stock into a substantially non-hydratable state before it is subjected to reduction or disintegration in water in a beater engine, wherefore, hydration or gelatinization of the stock is inhibited-during the beating operation and the resulting pulp or halfstuif can be formed into water-laid felts characterized by their high absorbency, softness, and flexibility.

riety, to form impregnated products of a high binder content and characterized by a highly desirable combination of characteristics. The felt a may, for example, be bituminized to form a sheet which is highly pliant and practically proof against tear, especially the initiation of tear. Apparently, the fact that the contiguous fibers in the sheet are not bonded strongly by hydrated cellulose is responsible for the high tear resistance in the bituminized sheet, since 'it is quite likely that when a tearing stress is applied to-the sheet, the stress,rather than becoming localized and giving rise to rupture of the sheet, is not. confined to any particular locus, but is distributed and/ or dissipated over a large area on account ofthe freedom of the fibers to slip or move past one another.

While various chemical reagents may be used to convert the raw rag stock to a substantially non-hydratable state, I have found that a' most effective and practical way of accomplishing this result is to subject the rag stock to the action of mercerizing liquors for a sufiicient period of time to mercerize the cellulose and thereby make it non-hydratable- In using the term "mercer- "izef, I mean that the stock undergoes the action 'of a caustic soda solution whose activity is preferably that of aybaustic soda solution of at least about 18% strength at room temperature, al though the term is meant to embrace the use of solutions whose activity corresponds to a caustic soda solution of about 10% strength at room temperature, as such latter solutions, while they do 7 not mercerize to completion, nevertheless change the cellulose fiber structure so .as to make it difficultly hydratable; An important advantage .40 gained through the use of a mercerizing liquor, besides that of transforming the cellulose to a non-hydratable state, isthat it functions as a cleansing or purifying agent, tending .to dissolve degraded cellulose, and other impurities foreign to or. inherent in rag stock.

A specific treatment to be applied in accordance with my invention to rag stock may involve mixing of the rag stock as it is purchased on the open market with a solution of caustic soda of about 18% or greater strength at room or below room temperature. The rags may be mixed with suflicient solution, say, about 10 or more parts by weight of solution to 1 part by weight of dry rags, to en ure sufflcient liquor to cover or subsulphide.

merse the rags, and the mixture may be gently st irred over a period of, say, 30, minutes to 6 hours. Under such conditions, the rag stock becomes mercerized and purified, the extent of mercerization and purification depending upon the duration of the treatment. After the treatment, the mercerizing liquor may be separated from the rag stock, as in a counter-current washer designed to efi'ect washing of the stock with minimum dilution of the liquor so that the liquor may be re-used in the treatment of other raw rag stock. If desired, rather than washing the stock free from mercerizing liquor, the excess liquor may be separated without dilution as in a centrifuge, thickener, or other filtering or separating apparatus. A portion of the liquor, in'fact, most of the liquor, may thus be recovered in an undiluted condition and be re-used with little, if any, fortification in the treatment of other raw rag stock. The centrifuged or thickened rag stock may then be washed free of the residual mercerizing liquor as hereinbefore described.

When the rag stock is treated at temperatures below normal or room temperature, the causticity I of the liquor requisite for. the mercerization of the stock may be lower than the 18% caustic containing as little as about caustic soda. It

is, in fact, possible to operate at temperatures below the freezing point, in which case, mercerization may be effected with even more dilute caustic soda solution, as in such case, ice or water crystals separate out from the solution, in consequence of which the unfrozen "or liquid portion of the solution becomes more concentrated in caustic soda and functions more eflectiv'ely as a mercerizing agent. In the event that the treatment of the rag stock is performed with a refrigerated or partially frozen mercerizing liquor, it is of de-' cided advantage to separate out the excess refrigerated liquor from the stock so as to conserve it in a refrigerated as well as undiluted condition for the treatment of other raw rag stock.

.Should'a portion of the mercerizing liquor be frozen, it may be thawed out to-permit a separation of as much liquor as possible from the stock, before the stock is washed.

The alkaline liquor used for the purpose of the present invention may, if desired, contain alkalies other than caustic soda, for instance, sodium kraft pulp mill, which, as is well known, contains sodium sulphide as well as caustic soda, may be employed under mercerizing conditions, as hereinbefore defined. So, too, the mercerizing liquor may contain suitable oxidants, such as'hypochlorite bleach, sodium peroxide, hydrogen peroxide, permanganate, or the like. An oxidant should not, however, be usedin the mercerizing liquor when a reducing agent like sodium sulphide is present therein. A mercerizing liquor containing an oxidant is of value more particularly in connection with colored rag stock, as it makes possible partial or complete decolorization of the rags, so that the halfs'tuif or pulp subsequently produced therefrom maybe fabricated.

into felts of lighter color, when such latter tional oxidant.

Thus, the so-called white liquor of a 1,9e7,a1a

quality is a de'sideratum. The fact is, that in.

some cases it may be advantageous to treat the rags with oxidants such as chlorine, hypochlorite bleach, permanganate, or the like, and then to wash the rags before they are treated in a mercerizing liquor containing, if desired, addi- The washed, mercerized rag stock prepared as hereinbefore described may be charged into a hollander or beater engine together with sufiicient water to ensure circulation and then reduced or beaten by the operation of the engine into a pulp or halfstufl fit for delivery to a felt-making sulting felts reflect the freeness of the pulp furnish from which they have been prepared in that they are comparatively tender or lacking in tensilestrength and tear resistance and in that they are highly porous, bibulous, soft and flexible. When impregnated with binders, how-' ever, these felts ,acquire enormous toughness,

strength and tear resistance. For instance, they become leatherlike in their properties when they are impregnated with rubber. latex, rubber solutions or the like, and are then dried. They become tough, pliant, and practically tear-proof when they are impregnated with bitumen or similar binders in the production of roofing and floorcovering materials.

In making the water-laid felts or foundations of the present invention, it may be of advantage to 'admix with the substantially unhydrated rag pulp or halfstuif, a suitable proportion of unmercerized cellulose pulp which may be in a substantially unhydrated, partially hydrated, or well-hydrated condition. The well-hydrated pulp blended with the mercerized rag pulp or halfstuff may be prepared by overbeating rag stock or other suitable cellulose fiber in much the same way as is' done in connection with the manufacture of glassine papers. The best kinds of hydrated or gelatinized celluloses for blending with the mercerized rag pulp or halfstuff are vthose prepared in a so-called stone-roll beater from kraft or other wood pulps which have been refined by alkali to higher alpha cellulose content. The use of some unmercerized pulp facilitates the production of uniformly-textured felts,

serving to offset the clumping or bunching tendencies in mercerized pulp. It is, however, possible to avoid clumpy or non-uniform felt formation. evenwhen the entirefelt-making furnish is mercerized by delivering the furnish in an extremely dilute and well-mixed'condition to the felt-forming machine. The use of hot water as a suspending medium for the felt-making furnish also mitigates the clumping or bunching tendencies of the mercerized fibers.

Since the present invention is centered about the use of rag stock as a felt-making raw material, it is well to define what I mean by rag stock. In using the expressions "rags or rag stock, I mean cellulose fiber occurring in the form of woven and/or knitted fabric or strand material such as-cloth, burlap, rope, or the like, made up of cotton, linen, jute, or similar cellulosic fiber yarns which must be disintegrated or reduced to form a comparatively short-fibered pulp or halfstuif before satisfactory formation into felts can be realized on machinery of the paper-making type. In some instances, the rags may contain non-cellulo sic fibers, such as wool and/or silk,- but inasmuch as these are largely is performed before the rags are mercerized and the mercerizing liquor is washed therefrom.

While my entire process, including mercerization and washing, might be performed in a beater engine, nevertheless, during the initial stages of the process, that is, ,before the stock has been mercerized to a non-hydratable condition, the beater roll should not be operated to beat or reduce thestock but merely to, efiect circulation and mixing; otherwise, considerable cellulose would be lost on account of. initial hydrating tendencies become substantially non-hydratable that I' and the loss of the hydrated cellulose in the mercerizing liquor. It is only after the stock has lower the beater roll to effect a cutting or reducing action of any moment. Indeed, I prefer to efiect such beating or reducing action after the mercerizing liquor has been substantially completely removed or washed from the stock.

Another important advantage-inhering in my invention is that when rag stock is treated with strong alkaline liquor substantially without disintegration or reduction of the rags into fibers or fiber, fragments, the recovery of the unused alkali is facilitated because it is much easier to remove the alkaline liquor from rags, as hereinbefore described, than from a mass of fibers or pulp dispersed in an alkaline liquor. f

I claim: I

1. A process which comprises converting rags to a substantially non-hydratable condition substantially without disintegrating or reducing them, and then mechanically reducing the nonhydratable rags in water to'form a substantially ungelatinized pulp or halfstuif consisting of fibers feltable into a uniform texture.

2. A process which comprises treating rags with a mercerizing liquor substantially without disintegrating or reducing them, thereby converting them into a mercerized, substantially non-hydratable condition, and beating the rags in water to form a substantially u'ngelatinized pulp ,or halfstufi consisting of fibers feltable into a uniform texture.

3. A process which comp es converting rags toa substantially non-hydra ble condition substantiallywithout disintegrating or mechanically reducing them, reducing the non-hydratable rags inwater to form a substantially ungelatinized pulp or halfstuif consisting of fibers feltable into a uniform texture, and forming such pulp Y or halfstuif into a water-laid felt.

4. A process which comprises treating rags with a mercerizing liquor substantially without'disina water-laid felt.

tegrating or reducing them, thereby converting them into a mercerized, substantially nonlrydratable condition, beating the rags in water to form a substantially ungelatinized pulp or halfstuif consisting of fibers feltable into a uniform texture, and forming suchpulp or halfstufl into 5. A process which comprises treating rags with a mercerizing liquor substantially without disintegrating or reducing them, thereby converting them into a mercerized, substantially nonhydratable condition, removing the mercerizing liquor from the rags, beating the rags in water to form a substantially ungelatinizedpulp or halftexture, and forming such pulp or halfstufl into a water-laid felt.

6. A process which comprises treating rags with an ,oxidant, and then treating the rags with a stuff consisting of fibers feltable into a uniform mercerizing liquor containing an oxidant substantially without disintegrating or. reducing them, thereby converting them into a mercerized, substantially 'non-hydratable condition, and heating the rags in water to form a pulp or halfstuff liquor substantially without disintegrating or reducing them, thereby converting them into a mercerized, substantially non-hydratable condition, and beating the rags in water to form a pulp or halfstuff consisting of'fibers feltable into a uniform texture.

9. A process which comprises treating rags with a mercerizing liquor containing an oxidant subv stantially without disintegrating or reducin them, thereby converting them into a mercerized, substantially non-hydratable condition, beating the rags in water to form a pulp or halfstufi consistingof fibers feltable into a uniform texture, and forming such pulp or halfstuif into a waterlaid felt.

10. A process which comprises treating rags with a mercerizing liquor substantially without i disintegrating or reducing them, thereby converting them into amercerized, substantially nonhydratable condition, beating the rags in water to form a substantially un'gelatinized but mercerized pulp or halfstufi consisting of fibers feltable into a uniform texture, admixing unmercerized pulp with such mercerized pulp or halfstuff, and forming the mixture into a water-laid felt.

11. A process which comprises treating rags with a mercerizing liquor containing sodium sulphide while maintaining them in a substantially unreducedv condition, and beating the resulting mercerized rags in water to form a substantially ungelatinized pulp consisting of fibers feltable into 

